顶部电离层Pc3压缩波的波动特征

基于2014年至2017年SWARM三颗卫星四年的磁场观测数据,我们挑选出Pc3压缩波事件,研究了顶部电离层Pc3压缩波活动强度的磁纬-磁地方时分布、随磁地方时变化的季节特征以及地理经纬度分布,并进一步分析了Pc3压缩波发生频次的分布特征.结果表明,中高纬和低纬的Pc3压缩波可能存在不同的激发机制.中高纬地区的扰动强度随高度衰减,且高纬地区几乎所有地方时都可以观测到Pc3压缩波,可能主要是由入射的阿尔芬波与电离层相互作用产生;而低纬地区扰动强度没有明显的高度依赖性且主要发生日侧,可能主要是上游波以快模波的形式直接传播到电离层所致.同时,该研究结果给出了入射阿尔芬波和电离层相互作用耦合产生Pc3压缩波理论模型的观测证据.

Characteristics of Pc3 compressional waves in the topside ionosphere

Based on SWARM observations from 2014 to 2017,we select Pc3 compressional waves and investigate the spatial and temporal distribution characteristics of Pc3 compressional waves in the topside ionosphere.The occurrence rates of Pc3 compressional wave are also analyzed.The results of statistical analysis reveal that there might be different excitation mechanism for Pc3 compressional wave at low latitude and higher latitude.We find that the decay of the amplitude of the Pc3 signal with altitude in the topside ionosphere at mid latitude and high latitude and there are high levels of Pc3 activity for all MLTs at high latitude.However,there is no obvious dependence on altitude for the amplitude of the Pc3 signal at low latitude and the main wave activity occurs on the dayside.It is suggested that the Pc3 compressional waves at mid latitude and high latitude might be the reflected fast magnetosonic mode excited by the interaction of the Alfvén wave with the ionosphere,while the waves at low latitude mainly caused by the transport of ULF wave energy from a distant magnetospheric source to the ionosphere occurs predominantly via the fast mode.This study provides the in situ observational evidence of compressional mode Pc3 waves induced by Alfvén waves incident on an inductive ionosphere in accordance with recent models.